There is interest in the development of specialized microparticles for use as adsorbents, chromatographic materials, cosmetic additives, matting agents, and permeable layers in multilayer imaging media. Irregularly shaped microparticles, wrinkled particles in particular, provide specific advantages of greater surface area and increased interstitial volume. This makes such particles particularly well suited for use in inkjet receiver media. For this application, there is additional interest in irregularly shaped particles of chemical compositions which lend inherent stability to guest dyes and colorants. It is also desirable that such particles have excellent colloidal stability in water and highly polar solvents.
In a typical inkjet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof
An inkjet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-forming layer and includes those intended for reflection viewing, which have an opaque support, and those intended for viewing by transmitted light, which have a transparent support.
An inkjet recording element that simultaneously provides an almost instantaneous ink dry time and good image quality is desirable. However, given the wide range of ink compositions and ink volumes that a recording element needs to accommodate, these requirements of inkjet recording media are difficult to achieve simultaneously.
Inkjet recording elements are known that employ porous or nonporous single layer or multilayer coatings that act as suitable ink receiving layers on one or both sides of a porous or non-porous support. Recording elements that use non-porous coatings typically have good image quality and stability but exhibit poor ink dry time. Recording elements that use porous coatings typically contain colloidal particulates and have poorer image stability but exhibit superior dry times.
While certain types of wrinkled particles are known which could conceivably be used in image recording elements for use with inkjet printing, there are many unsolved problems in the art and many deficiencies in the known products which limit their commercial usefulness. A major challenge in the design of an image-recording layer comprising wrinkled particles is to be able to obtain coatings which dry rapidly and impart favorable fade characteristics to guest colorants. Inkjet prints, prepared by printing onto inkjet recording elements, are subject to environmental degradation. They are especially vulnerable to light fade and fade resulting from gaseous impurities in the air, such as ozone and nitrogen oxides. Highly swellable hydrophilic layers can take an undesirably long time to dry, slowing printing speed. Porous layers speed the absorption of the ink vehicle, but often suffer from insufficient gloss and severe dye fade.
Irregularly shaped microparticles are known in the art, but they are badly suited for specific imaging applications due to either their size or composition or their inherent difficulty in preparation. WO 92/16565 and 93/19099 report crosslinked, wrinkled particles comprised of ethylenically unsaturated carboxylic acid-containing monomers. These particles, however, are large in size (>75 micrometers) and thus are unsuitable for use in thin coatings. In addition, the monomeric composition is chemically aggressive and will hasten the fade of guest dyes and colorants, thus making these particles unsuitable for certain imaging applications. Finally, the liquid uptake of these materials is extremely large. The particles increase dramatically in size upon absorbing liquids. Thus, coatings comprised of such superabsorbants will lose wet cohesion due to the large dimensional changes of the particles upon absorption of liquids. Bowl-shaped, crosslinked vinyl microparticles are reported in U.S. Pat. No. 5,559,202. The chemical composition of these particles, however, does not afford stability advantages to adsorbed dyes and colorants, thus making these particles unsuitable for use in inkjet receiver media. Wrinkled and irregularly shaped particles comprising methacrylate monomers are disclosed in Journal of Polymer Science Part A: Polymer Chemistry, Vol. 38, p. 4038–4056 (2000). Similarly, the chemical composition of these particles, does not afford stability advantages to adsorbed dyes and colorants, thus making these particles unsuitable for use in inkjet receiver media.
There is a need to provide microparticles which are readily dispersible in water and highly polar solvents, show rapid fluid absorption when incorporated in inkjet receiver media, and which are comprised of materials which lend inherent stability to guest colorants.